1. Field of the Invention
The present invention relates to an antenna module, and in particular relates to an antenna module having an Electromagnetic Band Gap cover.
2. Description of the Related Art
FIG. 1a shows a conventional antenna module 1, comprising a cover 10, an antenna substrate 20 and an antenna 30. The antenna 30 provides a wireless signal 2. The cover 10 increases reflection number of times of the wireless signal 2 to increase the energy intensity thereof. The cover 10 has a first reflection phase angle Φ1, and the antenna substrate 20 has a second reflection phase angle Φ2. The first reflection phase angle Φ1 is about −180°. The second reflection phase angle Φ2 is about −180°. To regulate the reflected wireless signal 2 in a phase, the following formula (A) may be utilized:
                              -                      (                                          360                λ                            ⁢              d              ⁢                                                          ⁢              1              ×              2                        )                          =                                            ϕ              1                        +                          ϕ              2                                =                                    -              360                        ×            N                                              (        A        )            According to the formula (A), a distance d1 between the cover 10 and the antenna substrate 20 is at least equal to half of a wavelength of the wireless signal 2.
FIG. 1b shows another conventional antenna module 1′, comprising a cover 10, an antenna substrate 20′ and an antenna 30. The antenna 30 provides a wireless signal 2. The cover 10 increases reflection number of times of the wireless signal 2 to increase the energy intensity thereof. The cover 10 has a first reflection phase angle Φ1, and the antenna substrate 20′ has a second reflection phase angle Φ2′. The first reflection phase angle Φ1 is about −180°. The second reflection phase angle Φ2′ is about 0°. To regulate the reflected wireless signal 2 in a phase, a distance d2 between the cover 10 and the antenna substrate 20′ is at least equal to a quarter of a wavelength of the wireless signal 2.
Conventionally, the distance between the cover 10 and the antenna substrate 20(20′) is large, and the volume of the antenna module is thus large.